Spectrally Confined Waveforms for Solid-State Transmit Modules

Abstract

Navy Radar operations are being curtailed in many littoral environments. This is due to two factors: the encroachment of telecommunication systems into the Navy radar bands and inband interference from other radars. The spectral widths of most pulsed radars are significantly wider than necessary with the present modulation schemes. Most radars utilize some form of constant-envelope pulse with phase or frequency modulation. This causes the spectrum to broaden several times the information bandwidth. If both the amplitude and phase of the transmitted signal are allowed to change, a significantly narrower bandwidth can be achieved. In this paper a method to create waveforms with instantaneous bandwidths of 20 MHz confined within −100 dB from sampled waveforms are presented. The kernel used as the interpolation function of a finite sampled time sequence is critical to the generation of a continuous time-domain signal that decays rapidly enough such that the leading and trailing tails are insignificant. This is important so that the radar is not transmitting a small amount of power for a long time which will significantly decrease the efficiency of the transmitter, thereby consuming a large amount of prime power. Although the autocorrelation function of the continuous narrowed waveform may be the same as the discrete autocorrelation function, some differences associated with the kernel used to create the waveform arise.